Data transmission method for HSDPA

ABSTRACT

In the data transmission method of an HSDPA system according to the present invention, a transmitter transmits Data Blocks each composed of one or more data units originated from a same logical channel, and a receiver receives the Data Block through a HS-DSCH and distributes the Data Block to a predetermined reordering buffer. Since each Data Block is composed of the MAC-d PDUs originated from the same logical channel, it is possible to monitor the in-sequence delivery of the data units, resulting in reduction of undesirable queuing delay caused by logical channel multiplexing.

This application is a continuation of U.S. patent application Ser. No.12/568,570 filed on Sep. 28, 2009, now U.S. Pat. No. 7,924,879, issuedon Apr. 12, 2011, which is a continuation of U.S. patent applicationSer. No. 12/146,351 filed on Jun. 25, 2008, now U.S. Pat. No. 8,238,342,issued on Aug. 7, 2012, which is a continuation of U.S. patentapplication Ser. No. 10/334,704 filed on Jan. 2, 2003 now U.S. Pat. No.7,403,541, issued on Jul. 22, 2008, and also claims the benefit ofearlier filing date and right of priority to Korean Application No.00630/2002 filed on Jan. 5, 2002, the contents of all of which arehereby incorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system and,more particularly, to a method for reducing the transmission delay ofpacket data in a mobile radio communication system.

2. Description of the Background Art

A universal mobile telecommunications system (UMTS) is a thirdgeneration mobile communication system that has evolved from a standardknown as Global System for Mobile communications (GSM). This standard isa European standard which aims to provide an improved mobilecommunication service based on a GSM core network and wideband codedivision multiple access (W-CDMA) technology. In December, 1998, theETSI of Europe, the ARIB/TTC of Japan, the T1 of the United States, andthe TTA of Korea formed a Third Generation Partnership Project (3GPP)for the purpose of creating the specification for standardizing theUMTS.

The work towards standardizing the UMTS performed by the 3GPP hasresulted in the formation of five technical specification groups (TSG),each of which is directed to forming network elements having independentoperations. More specifically, each TSG develops, approves, and managesa standard specification in a related region. Among them, a radio accessnetwork (RAN) group (TSG-RAN) develops a specification for the function,items desired, and interface of a UMTS terrestrial radio access network(UTRAN), which is a new RAN for supporting a W-CDMA access technology inthe UMTS.

The TSG-RAN group includes a plenary group and four working groups.Working group 1 (WG1) develops a specification for a physical layer (afirst layer). Working group 2 (WG2) specifies the functions of a datalink layer (a second layer) and a network layer (a third layer). Workinggroup 3 (WG3) defines a specification for an interface among a basestation in the UTRAN, a radio network controller (RNC), and a corenetwork. Finally, Working group 4 (WG4) discusses requirements desiredfor evaluation of radio link performance and items desired for radioresource management.

FIG. 1 shows a structure of a 3GPP UTRAN. This UTRAN 110 includes one ormore radio network sub-systems (RNS) 120 and 130. Each RNS 120 and 130includes a RNC 121 and 131 and one or more Nodes B 122 and 123 and 132and 133 (e.g., a base station) managed by the RNCs. RNCs 121 and 131 areconnected to a mobile switching center (MSC) 141 which performs circuitswitched communications with the GSM network. The RNCs are alsoconnected to a serving general packet radio service support node (SGSN)142 which performs packet switched communications with a general packetradio service (GPRS) network.

Nodes B are managed by the RNCs, receive information sent by thephysical layer of a terminal 150 (e.g., mobile station, user equipmentand/or subscriber unit) through an uplink, and transmit data to aterminal 150 through a downlink. Nodes B, thus, operate as access pointsof the UTRAN for terminal 150.

The RNCs perform functions which include assigning and managing radioresources. An RNC that directly manages a Node B is referred to as acontrol RNC (CRNC). The CRNC manages common radio resources. A servingRNC (SRNC), on the other hand, manages dedicated radio resourcesassigned to the respective terminals. The CRNC can be the same as theSRNC. However, when the terminal deviates from the region of the SRNCand moves to the region of another RNC, the CRNC can be different fromthe SRNC. Because the physical positions of various elements in the UMTSnetwork can vary, an interface for connecting the elements is necessary.Nodes B and the RNCs are connected to each other by an lub interface.Two RNCs are connected to each other by an lur interface. An interfacebetween the RNC and a core network is referred to as lu.

FIG. 2 shows a structure of a radio access interface protocol between aterminal which operates based on a 3GPP RAN specification and a UTRAN.The radio access interface protocol is horizontally formed of a physicallayer (PHY), a data link layer, and a network layer and is verticallydivided into a control plane for transmitting a control information anda user plane for transmitting data information. The user plane is aregion to which traffic information of a user such as voice or an IPpacket is transmitted. The control plane is a region to which controlinformation such as an interface of a network or maintenance andmanagement of a call is transmitted.

In FIG. 2, protocol layers can be divided into a first layer (L1), asecond layer (L2), and a third layer (L3) based on three lower layers ofan open system interconnection (OSI) standard model well known in acommunication system.

The first layer (L1) operates as a physical layer (PHY) for a radiointerface and is connected to an upper medium access control (MAC) layerthrough one or more transport channels. The physical layer transmitsdata delivered to the physical layer (PHY) through a transport channelto a receiver using various coding and modulating methods suitable forradio circumstances. The transport channel between the physical layer(PHY) and the MAC layer is divided into a dedicated transport channeland a common transport channel based on whether it is exclusively usedby a single terminal or shared by several terminals.

The second layer L2 operates as a data link layer and lets variousterminals share the radio resources of a W-CDMA network. The secondlayer L2 is divided into the MAC layer, a radio link control (RLC)layer, a packet data convergence protocol (PDCP) layer, and abroadcast/multicast control (BMC) layer.

The MAC layer delivers data through an appropriate mapping relationshipto between a logical channel and a transport channel. The logicalchannels connect an upper layer to the MAC layer. Various logicalchannels are provided according to the kind of transmitted information.In general, when information of the control plane is transmitted, acontrol channel is used. When information of the user plane istransmitted, a traffic channel is used. The MAC layer is divided twosub-layers according to performed functions. The two sub-layers are aMAC-d sub-layer that is positioned in the SRNC and manages the dedicatedtransport channel and a MAC-c/sh sub-layer that is positioned in theCRNC and manages the common transport channel.

The RLC layer forms an appropriate RLC protocol data unit (PDU) suitablefor transmission by the segmentation and concatenation functions of anRLC service data unit (SDU) received from an upper layer. The RLC layeralso performs an automatic repeat request (ARQ) function by which an RLCPDU lost during transmission is re-transmitted. The RLC layer operatesin three modes, a transparent mode (TM), an unacknowledged mode (UM),and an acknowledged mode (AM). The mode selected depends upon the methodused to process the RLC SDU received from the upper layer. An RLC bufferstores the RLC SDUs or the RLC PDUs received from the upper layer existsin the RLC layer.

The packet data convergence protocol (PDCP) layer is an upper layer ofthe RLC layer which allows data items to be transmitted through anetwork protocol such as the IPv4 or the IPv6. A header compressiontechnique for compressing and transmitting the header information in apacket can be used for effective transmission of the IP packet.

The broadcast/multicast control (BMC) layer allows a message to betransmitted from a cell broadcast center (CBC) through the radiointerface. The main function of the BMC layer is scheduling andtransmitting a cell broadcast message to a terminal. In general, data istransmitted through the RLC layer operating in the unacknowledged mode.

The PDCP layer and the BMC layer are connected to the SGSN because apacket switching method is used, and are located only in the user planebecause they transmit only user data. Unlike the PDCP layer and the BMClayer, the RLC layer can be included in the user plane and the controlplane according to a layer connected to the upper layer. When the RLClayer belongs to the control plane, data is received from a radioresource control (RRC) layer. In the other cases, the RLC layer belongsto the user plane. In general, the transmission service of user dataprovided from the user plane to the upper layer by the second layer (L2)is referred to as a radio bearer (RB). The transmission service ofcontrol information provided from the control plane to the upper layerby the second layer (L2) is referred to as a signaling radio bearer(SRB). As shown in FIG. 2, a plurality of entities can exist in the RLCand PDCP layers. This is because a terminal has a plurality of RBs, andone or two RLC entities and only one PDCP entity are generally used forone RB. The entities of the RLC layer and the PDCP layer can perform anindependent function in each layer.

The RRC layer positioned in the lowest portion of the third layer (L3)is defined only in the control plane and controls the logical channels,the transport channels, and the physical channels in relation to thesetup, the reconfiguration, and the release of the RBs. At this time,setting up the RB means processes of stipulating the characteristics ofa protocol layer and a channel, which are required for providing aspecific service, and setting the respective detailed parameters andoperation methods. It is possible to transmit control messages receivedfrom the upper layer through a RRC message.

The aforementioned W-CDMA system attempts to achieve a transmissionspeed of 2 Mbps indoors and in a pico-cell circumstance, and atransmission speed of 384 kbps in a general radio condition. However, asthe wireless Internet becomes more widespread and the number ofsubscribers increases, more diverse services will be provided. In orderto support these services, it is expected that higher transmissionspeeds will be necessary. In the current 3GPP consortium, research isbeing performed to provide high transmission speeds by developing theW-CDMA network. One representative system is known as the high-speeddownlink packet access (HSDPA) system.

The HSDPA system is based on WCDMA. It supports a maximum speed of 10Mbps to the downlink and is expected to provide shorter delay time andan improved capacity than existing systems. The following technologieshave been applied to the HSDPA system in order to provide highertransmission speed and enlarged capacity: link adaptation (LA), hybridautomatic repeat request (HARQ), fast cell selection (FCS), and multipleinput, multiple output (MIMO) antenna.

The LA uses a modulation and coding scheme (MCS) suitable for thecondition of a channel. When the channel condition is good, high degreemodulation such as 16QAM or 64QAM is used. When the channel condition isbad, low degree modulation such as QPSK is used.

In general, low degree modulation methods support a lesser amount oftransmission traffic than high degree modulation methods. However, inlow degree modulation methods, a transmission success ratio is high whena channel condition is not desirable and therefore, it is advantageousto use this form of modulation when the influences of fading orinterference is large. On the other to hand, frequency efficiency isbetter in high degree modulation methods than in low degree modulationmethods. In the high degree modulation methods, it is possible, forexample, to achieve a transmission speed of 10 Mbps using the 5 MHzbandwidth of W-CDMA. However, high degree modulation methods are verysensitive to noise and interference. Therefore, when a user terminal islocated close to a Node B, it is possible to improve transmissionefficiency using 16QAM or 64QAM. And, when the terminal is located onthe boundary of the cell or when the influence of fading is large, lowmodulation method such as QPSK is useful.

The HARQ method is a re-transmission method which differs from existingre-transmission methods used in the RLC layer. The HARQ method is usedin connection with the physical layer, and a higher decoding successratio is guaranteed by combining re-transmitted data with previouslyreceived data. That is, a packet that is not successfully transmitted isnot discarded but stored. The stored packet is combined with are-transmitted packet in a step before decoding and is decoded.Therefore, when the HARQ method is used together with the LA, it ispossible to significantly increase the transmission efficiency of thepacket.

The FCS method is similar to a related art soft handover. That is, theterminal can receive data from various cells. However, in considerationof the channel condition of each cell, the terminal receives data from asingle cell which has the best channel condition. The related art softhandover methods increase the transmission success ratio usingdiversity, and more specifically, by receiving data from various cells.However, in the FCS method, data is received from a specific cell inorder to reduce interference between cells.

Regarding the MIMO antenna system, the transmission speed of data isincreased using various independent radio waves propagated in thedispersive channel condition. The MIMO antenna system usually consistsof several transmission antennas and several reception antennas, so thatdiversity gain is obtained by reducing correlation between radio wavesreceived by each antenna.

The HSDPA system, thus, to adopt a new technology based on a WCDMAnetwork. However, in order to graft new technologies, modification isunavoidable. As a representative example, the function of Node B isimproved. That is, though most control functions are located in the RNCin a WCDMA network, new technologies for the HSDPA system are managed bythe Node B in order to achieve faster adjustment to the channelconditions and to reduce a delay time in the RNC. The enhanced functionof the Node B, however, is not meant to replace the functions of the RNCbut rather is intended to supplement these functions for high speed datatransmission, from a point of view of the RNC.

Thus, in an HDSPA system, the Nodes B are modified to perform some ofthe MAC functions unlike in the WCDMA system. A modified layer whichperforms some of the MAC function is referred to as a MAC-hs sub-layer.

The MAC-hs sub-layer is positioned above the physical layer and canperform packet scheduling and LA functions. The MAC-hs sub-layer alsomanages a new transport channel known as HS-DSCH (High Speed-DownlinkShared Channel) which is used for HSDPA data transmission. The HS-DSCHchannel is used when data is exchanged between the MAC-hs sub-layer andthe physical layer.

FIG. 3 shows a radio interface protocol structure for supporting theHSDPA system. As shown, the MAC layer is divided into a MAC-d sub-layer,a MAC-c/sh sub-layer, and a MAC-hs sub-layer. The MAC-hs sub-layer ispositioned above the physical layer (PHY) of a Node B. The MAC-c/sh andMAC-d sub-layers to are located in the CRNC and the SRNC. A newtransmission protocol referred to the HS-DSCH frame protocol (FP) isused between the RNC and the Node B or among the RNCs for the deliveryof HSDPA data.

The MAC-c/sh sub-layer, the MAC-d sub-layer, and the RLC layerpositioned above the MAC-hs sub-layer perform the same functions as thecurrent system. Therefore, a slight modification of the current RNC canfully support the HSDPA system.

FIG. 4 shows the structure of a MAC layer used in the HSDPA system. TheMAC layer is divided into a MAC-d sub-layer 161, a MAC-c/sh sub-layer162, and a MAC-hs sub-layer 163. The MAC-d sub layer in the SRNC managesdedicated transport channels for a specific terminal. The MAC-c/shsub-layer in the CRNC manages the common transport channels. The MAC-hssub-layer in the Node B manages the HS-DSCH. In this arrangement, thefunctions performed by the MAC-c/sh sub-layer 162 in the HSDPA systemare reduced. That is, the MAC-c/sh sub-layer assigns common resourcesshared by various terminals in the conventional system and processes thecommon resources. However, in the HSDPA system, the MAC-dish sub-layersimply performs a flow control function of the data delivery between theMAC-d sub-layer 161 and the MAC-hs sub-layer 163.

Referring to FIG. 4, it will be described how data received from the RLClayer is processed and delivered to the HS-DSCH in the MAC layer. First,the path of the RLC PDU delivered from the RLC layer through thededicated logical channel, (i.e. a dedicated traffic channel (DTCH) or adedicated control channel (DCCH)), is determined by a channel switchingfunction in the MAC-d layer. When an RLC PDU is delivered to thededicated channel (DCH), a related header is attached to the RLC PDU inthe MAC-d sub-layer 161 and the RLC PDU is delivered to the physicallayer through the DCH. When the HS-DSCH channel of the HSDPA system isused, the RLC PDU is delivered to the MAC-c/s h sub-layer 162 by achannel switching function. When a plurality of logical channels use onetransport channel, the RLC PDU passes through a transport channelmultiplexing block. The identification information (control/traffic(C/T) field) of the logical channel, to which each RLC PDU belongs, isadded during this process. Also, each logical channel has a priority.Data of a logical channel has the same priority.

The MAC-d sub-layer 161 transmits the priority of a MAC-d PDU when theMAC-d PDU is transmitted. The MAC-c/sh sub-layer 162 that received theMAC-d PDU simply passes the data received from the MAC-d sub-layer 161to the MAC-hs sub-layer 163. The MAC-d PDU delivered to the MAC-hssub-layer 163 is stored in the transmission buffer in the schedulingblock. One transmission buffer exists per each priority level. EachMAC-hs SDU (MAC-d PDU) is sequentially stored in the transmission buffercorresponding to its priority.

An appropriate data block size is selected by the scheduling functiondepending on the channel condition. Accordingly, a data block is formedby one or more MAC-hs SDUs.

A priority class identifier and a transmission sequence number are addedto each data block and each data block is delivered to the HARQ block.

A maximum 8 HARQ processes exist in the HARQ block. The data blockreceived from the scheduling block is delivered to an appropriate HARQprocess. Each HARQ process operates in a stop and wait (SAW) ARQ. Inthis method, the next data block is not transmitted until a current datablock is successfully transmitted. As mentioned above, because only onedata block is transmitted in a TTI, only one HARQ process is activatedin one TTI.

Another HARQ processes waits until its turn. Each HARQ process has aHARQ process identifier. A corresponding HARQ process identifier ispreviously known to the terminal through a downlink control signal, sothat a specific data block passes through the same HARQ process in thetransmitter (the UTRAN) and the receiver (the terminal). The HARQprocess that transmitted the data block also stores the data block toprovision the future re-transmission. The HARQ process, re-transmits thedata block when NonACKnowledge (NACK) is received from the terminal.

When ACK is received from the terminal, the HARQ process deletes thecorresponding data block and prepares the transmission of a new datablock. When the data block is transmitted, a transport format andresource combination (TFRC) block selects an appropriate TFC for theHS-DSCH.

FIG. 5 shows a structure of the MAC layer of the terminal used in theHSDPA system. This MAC layer is divided into a MAC-d sub-layer 173, aMAC-c/sh sub-layer 172, and a MAC-hs sub-layer 171. Unlike the UTRAN,the above three layers are located in the same place. The MAC-dsub-layer and the MAC-c/sh sub-layer in the terminal are almost same asthose in the UTRAN, but the MAC-hs sub-layer 171 is slightly differentbecause the MAC-hs sub-layer in the UTRAN performs only transmission andthe MAC-hs sub-layer in the terminal performs only reception.

The manner in which the MAC layer receives the data from the physicallayer and delivers it to the RLC layer will now be described. The datablock delivered to the MAC-hs sub-Payer 171 through the HS-DSCH is firststored in one of the HARQ processes in the HARQ block. In which processthe data block is to stored can be known from the HARQ processidentifier included in the downlink control signal.

The HARQ process, in which the data block is stored, transmits the NACKinformation to the UTRAN when there are errors in the data block andrequests the re-transmission of the data block. When no errors exist,the HARQ process delivers the data block to a reordering buffer andtransmits the ACK information to the UTRAN. A reordering buffer has apriority like the transmission buffer in the UTRAN. The HARQ processdelivers the data block to the corresponding reordering buffer with theaid of a priority class identifier included in the data block. Asignificant characteristic of the reordering buffer is that it supportsin-sequence delivery of data.

Data blocks are sequentially delivered to an upper layer based on atransmission sequence number (TSN). More specifically, when a data blockis received while one or more previous data blocks are missing, the datablock is stored in the reordering buffer and is not delivered to theupper layer. Rather, the stored data block is delivered to the upperlayer only when all previous data blocks are received and delivered tothe upper layer. Because several HARQ processes operate, a reorderingbuffer usually receives data blocks out of sequence. Therefore, anin-sequence delivery function is used for the reordering buffer so thatthe data blocks can be delivered to the upper layer sequentially.

One difference between the reordering buffer of the terminal and thetransmission buffer of the UTRAN is that the reordering buffer storesdata in units of data block which is composed of one or more MAC-hsSDUs, while the transmission buffer stores data in units of MAC-hs SDU(=MAC-d PDU). Because the MAC-d sub-layer 173 processes data in units ofMAC-d PDUs, when the reordering buffer of the terminal MAC-hs sub-layer171 delivers the data block to the MAC-d sub-layer 173, the reorderingbuffer must first disassemble the data block into the MAC-d PDUs andthen deliver them to the MAC-d sub-layer. The MAC-c/sh sub-layer 172passes the MAC-d PDUs received from the MAC-hs sub-layer 171 to theMAC-d sub-layer. The MAC-d sub-layer 173 that received the MAC-d PDUchecks the logical channel identifier (C/T field) included in each MAC-dPDU in the transport channel multiplexing block and delivers the MAC-dPDUs to the RLC through the corresponding logical channel.

FIG. 6 shows processes for transmitting and receiving a data block in anHSDPA system. The MAC-d PDUs are actually stored in a transmissionbuffer 180. However, for the sake of convenience, it is shown as a datablock (=one or more MAC-d PDUs). The sizes of the respective data blockscan vary. However, the sizes are shown to be the same because the datablocks for illustrative purposes. Also, it is assumed that eight HARQprocesses 181 through 188 exist.

The process includes transmitting data blocks to the receiver for datablocks having transmission sequence numbers from TSN=13 to TSN=22 in thetransmission buffer. A data block with a lower TSN is served first to anempty HARQ process. For example, as shown, the data block TSN=13 isdelivered to HARQ process #1 181, and data block TSN=14 is delivered toHARQ process #8. From this explanation, it is clear that the TSN is notrelated to the HARQ process number.

When the HARQ process receives an arbitrary data block, the HARQ processtransmits the data block to the receiver in a specific TTI and storesthe data block for re-transmission that might be performed later. Onlyone data block can be transmitted in a certain TTI. Accordingly, onlyone HARQ process is activated in a single TTI. The HARQ process thattransmitted the data block informs the receiver of its process numberthrough a downlink control signal which is transmitted through adifferent channel than that of the data block.

The reason why the HARQ process of the transmitter coincides with theHARQ process of the receiver is that a stop-and-wait ARQ method is usedby is each HARQ process pair. That is, HARQ process #1 181 thattransmitted data block TSN=13 does not transmit another data block untilthe data block is successfully transmitted. Because a receiver HARQprocess #1 191 can know that data is transmitted thereto for acorresponding TTI through the downlink control signal, the receiver HARQprocess #1 transmits the NACK information to the transmitter through anuplink control signal when the data block is not successfully receivedwithin a defined transmission time interval (TTI). On the other hand,when a data block is successfully received, the receiver HARQ process #1transmits the ACK information to the transmitter, and at the same timedelivers the corresponding data block to the reordering buffer accordingto the priority.

The reordering buffer exists per priority level. The HARQ process checksthe priority included in the header information of the data block anddelivers the data block to the reordering buffer according to thepriority. The data block delivered to the reordering buffer is thendelivered to the upper layer when all of the previous data blocks aredelivered to the upper layer. However, when one or more previous datablocks are not delivered to the upper layer, the data block is stored inthe reordering buffer 190. That is, the reordering buffer must supportin-sequence delivery of data blocks to the upper layer. A data blockthat is not delivered to the upper layer is stored in the reorderingbuffer.

To illustrate the foregoing, FIG. 6 shows that when data block TSN=14 isreceived but data block TSN=13 is not received, data block TSN=14 isstored in the reordering buffer until data block TSN=13 is received.When data block TSN=13 is received, both data blocks are delivered tothe upper layer in the order of TSN=13 and TSN=14. When the data blocksare delivered to the upper layer, they are disassembled in units ofMAC-d PDUs and are delivered as described above.

FIG. 7 is a data block (MAC-hs PDU) format adopted in the HSDPA system.As shown in FIG. 7, the data block consists of a MAC-hs header includingcontrol information and a MAC-hs payload carrying the upper layer PDU.

The MAC-hs header includes a Queue ID field and a TSN field, and theMAC-hs payload includes a plurality of MAC-hs SDUs (MAC-d PDUs). EachMAC-d PDU includes the C/T field and the MAC-d SDU (RLC PDU). The C/Tfield is included in the MAC-d PDU header if multiplexing on MAC isapplied, and it provides identification of the logical channel whenmultiple logical channels are carried on the same transport channel.Four bits are currently allocated for C/T field in order to identify upto 15 different logical channels (1111 is reserved). Since a radiobearer is usually mapped to one logical channel, the C/T field can befurther used for identification of radio bearer.

FIG X is a flowchart illustrating how to deliver the received datablocks to re-ordering buffer in UE side MAC-hs sublayer.

As shown in FIG X, the UE side MAC-hs establishes the reordering bufferaccording to the logical channel priority (SX1), and checks if a DataBlock is received from HARQ entity (SX2). If the Data Block is receivedfrom HARQ entity, the MAC-hs checks the logical channel priority field(SX3) and forwards the Data Block to the reordering buffer of samepriority (SX4). Then, the MAC-hs checks the sequence number of the DataBlock, i.e. TSN of the Data Block, (SX5), and determines whether theData Block can be delivered or not (SX6). If the Data Block isdetermined that it can be delivered, the MAC-hs disassembles the DataBlock into data units (SX7), and checks the logical channel identity ofeach data units by the C/T field (SX8). Each of the disassembled dataunits is then delivered is to the corresponding logical channel,respectively (SX9).

In step SX6, if the Data Block is determined that it can not bedelivered due to one or more missing Data Blocks preceding it, theMAC-hs stores the Data Block in the reordering buffer according to itssequence number instead of delivering it (SX10). After the Data Block isprocessed in the above manner, the UE side MAC-hs determines whether ornot the HS-DSCH connection is released (SX11). If the HS-DSCH connectionis not released, the algorithm goes to the step SX2.

FIG. 9 is an exemplary view for illustrating how data blocks consistingof MAC-d PDUs from different logical channels are transmitted in theHSDPA system.

In FIG. 9, 4 data blocks are transmitted from the UTRAN side MAC-hs. Forexample, Data Block #10 is composed of 3 MAC-d PDUs where 1 MAC-d PDU isoriginated from a logical channel #1 and 2 MAC-d PDUs originated from alogical channel #2. The figure illustrates the case when Data Block #10,#12, and #13 are successfully received by the UE side MAC-hs while Datablock #11 is lost during transmission. Since Data Block #10 has beensuccessfully received, the reordering buffer forwards the Data Block #10to the upper layer immediately. However, since Data Block #11 is notreceived, the correctly received Data Block #12 and #13 can not bedelivered to the upper layer but just stored in the reordering bufferuntil Data Block #11 is received or until some stall avoidance mechanismis terminated.

From the viewpoint of logical channel #2, the received MAC-d PDUs areseen as consecutive, since there are no missing MAC-d PDUs between thetwo adjacent MAC-d PDUs. In other words, since the Data Block #11 doesnot contain is any PDUs from logical channel #2, whether Data Block #11is received or not does not affect the in-sequence delivery of logicalchannel #2. Accordingly, if the reordering buffer knows the in-sequencedelivery of MAC-d PDUs of a specific logical channel, the MAC-d PDUs canbe immediately delivered to the upper layer without being delayed in thereordering buffer.

As described above, the multiplexing of logical channels has a drawbackin that delivery of MAC-d PDUs of one logical channel may beunnecessarily delayed due to a missing MAC-d PDU of other logicalchannel. Moreover, the delayed MAC-d PDUs sometimes become uselessbecause of the discards in the RLC layer.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to solve the aboveproblems.

It is an object of the present invention to provide a data transmissionmethod of HSDPA allowing the MAC-d PDU delay in the reordering buffer tobe minimized by monitoring the in-sequence delivery of MAC-d PDUsoriginated from the same logical channel.

It is another object of the present invention to provide a datatransmission method of HSDPA capable of enhancing the data transmissionby minimizing data processing delay in UTRAN (transmitter) and UE(receiver).

It is still another object of the present invention to provide a datatransmission method capable of minimizing transmission delay by quicklydelivering the data queued in the reordering buffer to the higher layer.

In one aspect of the present invention, the data transmission method forHSDPA system comprises transmitting, with a transmitter, a Data Blockcomposed of one or more data units originated from a same logicalchannel; receiving, with a receiver, the Data Block through a HS-DSCH;and distributing the Data Block to a predetermined reordering buffer.

The Data Block includes a transmission sequence number (TSN) field ofwhich value identifies Data Block and the data unit includes a controltraffic (C/T) field of which value identifies the logical channel.

The Data Block distribution to the reordering buffer is performed insuch a manner of checking the C/T field; distributing the Data Block tothe reordering buffer based on the value of the C/T field; checking theTSN field; and delivering the Data Block to higher layers when the DataBlock is determined an in-sequence Data Block or storing the Data Blockin a reordering buffer when the Data Block is determined as an out-ofsequence Data Block, based on the value of the TSN field. The out-ofsequence Data Block waits until a missed Data Block is received and thenthe Data Blocks in the reordering buffer are reordered if the missedData Block is received.

In another aspect of the present invention, the Data Block has atransmission sequence number (TSN) field of which value identifies DataBlock and a control traffic (C/T) field of which value identifies thelogical channel.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail with reference to thefollowing drawings in which like reference numerals refer to likeelements wherein:

FIG. 1 is a conceptual view showing a structure of a UMTS radio accessnetwork (UTRAN) of a 3GPP;

FIG. 2 is a conceptual view for showing a protocol structure of a radiointerface;

FIG. 3 is a conceptual view showing a structure of a radio interfaceprotocol for a high speed downlink packet access (HSDPA) system;

FIG. 4 is a conceptual view showing a UTRAN side MAC architecturesupporting the HS DPA system;

FIG. 5 is a block diagram of a UE side MAC architecture supporting theHSDPA system;

FIG. 6 is a conceptual view illustrating how data blocks are transmittedand processed in UTRAN side MAC-hs and UE side MAC-hs;

FIG. 7 is a drawing illustrating a conventional MAC-hs PDU format forHS-DSCH;

FIG. 8 is a flowchart illustrating a data delivery flow in UE sideMAC-hs for HSDPA according to a conventional method;

FIG. 9 is an exemplary view illustrating how data blocks multiplexedwith different logical channels are transmitted in the current HSDPAsystem;

FIG. 10 is a drawing illustrating a Data Block format for HS-DSCHadopted in the data transmission method according to a preferredembodiment of the present invention;

FIG. 11 is a flowchart illustrating a data delivery flow in UE sideMAC-hs to for HSDPA according to a preferred embodiment of the presentinvention; and

FIG. 12 is a drawing illustrating a Data Block format for HS-DSCHadopted in the data transmission method according to another preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described hereinafter with reference tothe accompanying drawings.

In the present invention, one reordering buffer is assigned for eachlogical channel so as to prevent the received data to be undesirablydelayed in the reordering buffer. That is, in the UTRAN side each DataBlock is composed of MAC-d PDUs originated from a single logical channelrather than MAC-d PDUs produced by multiplexing different logicalchannels.

A data transmission method according to a first preferred embodiment ofthe present invention will be described hereinafter with reference toFIG. 10 and FIG. 11.

FIG. 10 shows a Data Block format for HS-DSCH adopted in the datatransmission method according to the first preferred embodiment of thepresent invention.

As shown in the FIG. 10, the Data Block consists of a MAC-hs header anda MAC-hs payload. The MAC-hs header includes a TSN field but not apriority field, which exist in the conventional MAC-hs header, foridentifying the reordering buffer having a specific priority level. TheTSN of the MAC-hs header is unique to each logical channel and is usedto guarantee the in-sequence delivery of Data Blocks.

The MAC-hs payload consists of one or more MAC-hs SDUs (MAC-d PDUs)where each MAC-d PDU is composed of a C/T field and an RLC PDU. The C/Tfield is used for constructing the Data Block with MAC-d PDUs of samelogical channel. Accordingly, the C/T fields of all MAC-d PDUs in thesame Data Block are identical with each other.

Since the C/T fields of the MAC-d PDUs in each Data Block have the samevalue, the priority field, which exists in the conventional Data Block,for identifying the reordering buffer of UE side MAC-hs is not requiredany more. Accordingly, the Data Block format can be simpler than theconventional one.

FIG. 11 is a flowchart illustrating a data delivery flow in UE sideMAC-hs for HSDPA according to the first preferred embodiment of thepresent invention.

As shown in FIG. 10, the UE side MAC-hs establishes the reorderingbuffer according to the logical channel identity (S101), and checks if aData Block is received from HARQ entity (S102). If the Data Block isreceived from HARQ entity, the MAC-hs checks the logical channelidentity by the C/T field (S103) and forwards the Data Block to thereordering buffer associated with the indicated logical channel (S104).Then, the MAC-hs checks the sequence number of the Data Block, i.e. TSNof the Data Block, (S105), and determines whether the Data Block can bedelivered or not (S106). If the Data Block is determined that it can bedelivered, the MAC-hs disassembles the Data Block into data units(S107), and delivers all the data units to the logical channelassociated with the reordering buffer (S108). In this case, check oflogical channel identity for each data unit is not necessary, since allthe data units belong to the same logical channel which is closelyconnected to the reordering buffer.

In step S106, if the Data Block is determined that it can not bedelivered to due to one or more missing Data Blocks preceding it, theMAC-hs stores the Data Block in the reordering buffer according to itssequence number instead of delivering it (S109). After the Data Block isprocessed in the above manner, the UE side MAC-hs determines whether ornot the HS-DSCH connection is released (S110). If the HS-DSCH connectionis not released, the algorithm goes to the step SX2.

FIG. 12 shows a Data Block format for HS-DSCH adopted in the datatransmission method according to a second preferred embodiment of thepresent invention.

As shown in FIG. 12, the C/T field is included in the MAC-hs header notthe MAC-d PDU headers (=MAC-hs payload) and the MAC-hs payload consistsof RLC PDUs rather than MAC-d PDU. Since there is no logical channelmultiplexing and the data to be transmitted through each Data Block areoriginated from the same logical channel, only one C/T field per DataBlock is enough to distinguish the logical channel.

By constructing the Data Block format in this manner, the Data Blockformat can be much simpler than one of the first preferred embodiment.

As described above, in the data transmission method according to thepresent invention each Data Block is composed of the MAC-d PDUsoriginated from the same logical channel such that it is possible tomonitor the in-sequence delivery of MAC-d PDUs, resulting in reductionof undesirable queuing delay caused by logical channel multiplexing.

Also, since the data transmission method of the present invention canreduce the possibility of discard of the data to be transmitted in UTRANside by quickly delivering the data queued in reordering buffer to thehigher layer and to acknowledges to the UTRAN, resulting in enhancementof the data transmission performance.

While this invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not limited to thedisclosed embodiments, but, on the contrary, is intended to covervarious modifications and equivalent arrangements included within thespirit and scope of the appended claims.

What is claimed is:
 1. A method for processing a medium access control(MAC) protocol data unit (PDU) to be transmitted to a receiving devicein an acknowledgment mode, the method comprising: receiving a pluralityof service data units (SDUs) from an upper layer; combining theplurality of SDUs; assigning a sequence number to the combined pluralityof SDUs, wherein the sequence number is used for in-sequence delivery ofthe plurality of SDUs in the receiving device; adding a MAC header tothe combined plurality of SDUs to generate a MAC PDU, wherein the MACheader comprises an identifier and the sequence number, wherein theidentifier is common to the plurality of SDUs and is used by thereceiving device to map the received MAC PDU to a correspondingreordering buffer, and the corresponding reordering buffer of thereceiving device is configured according to the identifier; andtransmitting the generated MAC PDU to the receiving device.
 2. Themethod of claim 1, wherein the generated MAC PDU is stored in atransmission buffer.
 3. The method of claim 1, further comprisingretransmitting the generated MAC PDU if an acknowledgement message isnot received from the receiving device in the acknowledgement mode. 4.The method of claim 2, wherein one transmission buffer exists per eachidentifier.
 5. The method of claim 4, wherein the generated MAC PDU isdeleted from the transmission buffer when receiving an acknowledgementmessage from the receiving device.